Trim members

ABSTRACT

The application describes assemblies comprised of a body member in combination with a stainless steel trim member having a contact surface which abuts the body member and an exposure surface subject to view. Adhered to the contact surface and located between the contact surface and the body member is a layer of aluminum which provides galvanic protection for the body member. Covering the aluminum is a chromate or phosphate conversion coating which provides protection against aluminum galvanic corrosion without detrimentally affecting the galvanic protection which aluminum provides for the body member. Also described are conversion-coated, aluminum-striped stainless steel composites suitable for fabrication into trim members and a method for producing conversion-coated, aluminum-striped stainless steel trim members.

United States Patent 1151 3,6 Zaremski [451 Jan. 25, 1972 [54] TRIMMEMBERS Attorney-Richard A. Speer, Vincent G. Gioia and Howard R.

B k t k, [72] Inventor: Donald R. Zaremski, Cheswick, Pa. er ens 0c Jr[73] Assignee: Allegheny Ludlum Steel Corporation, Pitt- [57] ABSTRACTsburgh' The application describes assemblies comprised of a body [22]Filed; Sept 24 19 9 member in combination with a stainless steel trimmember Appl. No.: 860,541

Primary Examiner-L. Dewayne Rutledge Assistant ExaminerE. L. Weisehaving a contact surface which abuts the body member and an exposuresurface subject to view. Adhered to the contact surface and locatedbetween the contact surface and the body member is a layer of aluminumwhich provides galvanic protection for the body member. Covering thealuminum is a chromate or phosphate conversion coating which providesprotection against aluminum galvanic corrosion without detrimentallyaffecting the galvanic protection which aluminum provides for the bodymember. Also described are conversioncoated, aluminum-striped stainlesssteel composites suitable for fabrication into trim members and a methodfor producing conversion-coated, aluminum-striped stainless steel trimmembers.

12 Claims, 2 Drawing Figures PATENTED JAN25 I972 INVEN TOR. DONALD R.ZAREMSK/ Attorney TRIM MEMBERS The present invention relates tostainless steel composites in the form of trim members and moreparticularly to conversion-coated, aluminum-striped stainless steelcomposites in the form of trim members. It further relates toconversioncoated, aluminum-striped stainless steel composites suitablefor fabrication into trim members and to assemblies comprised ofconversion-coated, aluminum-striped stainless steel trim members incombination with body members.

Stainless steel is known to serve a particularly good purpose in thoseapplications where brightness and stain resistance to a variety ofcontaminants is required and is ideally suited for use as automotivetrim. However, since most automotive bodies are constructed of carbonsteel, the use of stainless steel can result in galvanic corrosion.Carbon steel is anodic to stainless steel and generally corrodes in thevicinity of stainless steel in the presence of an electrolyte, such asmoisture.

To protect carbon steel it has been the practice to coat stainlessstrips with a nonferrous sacrificial metal which is anodic to mildcarbon steel prior to or after forming the strips into trim members. Thecoating is preferably aluminum. It is applied to those sections of thestrip which will eventually contact the automotive body, i.e., thereturn flange of the fabricated trim member.

Testing under normal road conditions has indicated that the use ofaluminum solves the galvanic corrosion problem faced by automotivemanufacturers. However, when the aluminum corrodes, it results in theformation and bleeding of aesthetically objectionable aluminum corrosionproducts (white corrosion products).

I have discovered that the formation and bleeding of aluminum corrosionproducts can be minimized without adversely affecting the galvanicprotection provided by the aluminum, through application of a protectivechromate or phosphate conversion coating to the aluminum. These coatingshave been applied in nonrelated environments to aluminum for protectionagainst general corrosion and to very thin layers of zinc, forprotection against galvanic corrosion. My work has shown that they offerprotection against aluminum galvanic corrosion without detrimentallyaffecting the galvanic protection which aluminum provides for carbonsteel in the vicinity of stainless steel.

It is accordingly an object of this invention to provide aconversion-coated, aluminum-striped stainless steel composite.

It is a further object of this invention to provide an assemblycomprised of a body member in combination with a conversion-coated,aluminum-striped stainless steel trim member which provides galvanicprotection for the body member.

The foregoing and other objects of the invention will be best understoodfrom the following description, reference being had to the accompanyingdrawing, wherein:

FIG. 1 is a sectional view of a stainless steel trim member; and

FIG. 2 is a perspective view of a stainless steel trim member.

The present invention encompasses a composite suitable for fabricationinto a stainless steel trim member, a composite in the form of astainless steel trim member, a method for producing stainless steel trimmembers and an assembly comprising a stainless steel trim member incombination with a body member. The body member is comprised of metal,e.g., plain carbon steel, which is less noble in the electromotiveseries than stainless steel. In the context of this application, theterm metal is interpreted as including metal which is painted and coatedas well as bare.

The stainless steel trim member has a contact surface and an exposuresurface. The contact surface abuts the body member after assembly andthe exposure surface is subject to view. Adhered to the contact surfaceis a layer of aluminum. The aluminum is generally at least 0.5 of a milthick and preferably between 3 and 5 mils. Covering the aluminum is aconversion coating from the group consisting of chromate and phosphateconversion coatings.

FIGS. 1 and 2 are respectively a sectional and perspective view of astainless steel trim member 1 which meets the requirements of thisinvention. It comprises an exposed surface 2, contact surfaces 4,aluminum stripes 6, and conversion coatings 8.

The method of this invention includes the steps of shaping a stainlesssteel sheet into a trim member having an exposed surface and at leastone contact surface and adhering aluminum to those portions of the sheetwhich are the contact surfaces of the finally formed trim member. Any ofthe well-known methods of shaping, e.g., roll forming, and adhering;e.g., roll pressure bonding, are within the scope of this invention. Themethod additionally involves the step of applying a conversion coatingto the aluminum either before or after shaping. It can be any of thewell-known chromate or phosphate conversion coatings. A typical chromateconversion coating consists of 0.99 ounces of sodium dichromate, 0.132ounces of sodium fluoride, 0.66 ounces of potassium ferricyanide, 3cubic centimeters of nitric acid, and 1 gallon of water. It is appliedat a temperature between ambient and l30 F. for a period of time between5 seconds and 8 minutes. A typical phosphate conversion coating consistsof 1 gallon of water and 10-20 ounces of solution composed of 61.7percent ammonium phosphate, 22.9 percent ammonium fluoride, and 15.4percent potassium dichromate. It is applied at a temperature between 1l0 and 120 F. for a period of time between I and 5 minutes.

The following example illustrates several aspects of the invention.

A number of stainless steel trim members were prepared withstripes ofaluminum adhered to their contact surface. Half of the trim members wereassembled onto carbon steel body members without further treatment. Theother half were given a chromate conversion coating prior to assembly.Coating was accomplished by dipping the aluminum stripes into a bathmaintained at ambient temperature. Immersion times ranged from 1 to 3minutes. The bath contained Iridite No. l42, a chromate conversioncoating sold by Allied Research Products, Inc., Baltimore, Md.

All of the assemblies, i.e., those with and those without chromateconversion coatings, were subject to salt spray tests in order todemonstrate the effectiveness of the conversion coatings. These testsare considered to be accelerated tests insofar as they produce corrosiveconditions far more severe than those encountered by automotive bodiesunder normal road conditions. Aluminum corrosion products were well inevidence on the untreated assemblies, i.e., those without chromateconversion coatings, after 24 hours of testing. The treated assemblies,i.e., those with chromate conversion coatings, were essentially free ofaluminum corrosion products after hours of testing and provided thecarbon steel body member with galvanic protection equivalent to thatprovided by the untreated assemblies.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in connection with specificexamples thereof will suggest various other modifications andapplications of the same. It is accordingly desired that in construingthe breadth of the appended claims they shall not be limited to thespecific examples of the invention described herein.

Iclaim:

I. An assembly comprising a stainless steel trim member in combinationwith a first metal less noble in the electromotive series than stainlesssteel; said stainless steel trim member having an exposed surface and acontact surface abutting said first metal, a layer of aluminum adheringto said contact surface, said aluminum being less noble in theelectromotive series than said first metal, and a conversion coatingfrom the group consisting of chromate and phosphate conversion coatingson said aluminum. said coated aluminum acting to preclude galvanicaction between said first metal and said stainless steel.

2. An assembly according to claim 1 wherein said first metal is plaincarbon steel.

3. An assembly according to claim 1 wherein said conversion coating is achromate conversion coating.

4. An assembly according to claim I wherein said conversion coating is aphosphate conversion coating.

9. A composite article according to claim 7 wherein said conversioncoating is a phosphate conversion coating.

10. A composite article according to claim 7 having at least twospaced-apart stripes of aluminum.

II. A composite article according to claim 7 wherein said aluminum has athickness in excess of about 0.5 of a mil.

12. A composite article according to claim I] wherein said aluminum hasa thickness of from about 3 mils to about 5 mils.

2. An assembly according to claim 1 wherein said first metal is plaincarbon steel.
 3. An assembly according to claim 1 wherein saidconversion coating is a chromate conversion coating.
 4. An assemblyaccording to claim 1 wherein said conversion coating is a phosphateconversion coating.
 5. An assembly according to claim 1 wherein saidaluminum has a thickness in excess of about 0.5 of a mil.
 6. An assemblyaccording to claim 5 wherein said aluminum has a thickness of from about3 mils to about 5 mils.
 7. A composite article comprising: stainlesssteel, at least one stripe of aluminum adhered to said stainless steeland a conversion coating from the group consisting of chromate andphosphate conversion coatings on said aluminum.
 8. A composite articleaccording to claim 7 wherein said conversion coating is a chromateconversion coating.
 9. A composite article according to claim 7 whereinsaid conversion coating is a phosphate conversion coating.
 10. Acomposite article according to claim 7 having at least two spaced-apartstripes of aluminum.
 11. A composite article according to claim 7wherein said aluminum has a thickness in excess of about 0.5 of a mil.12. A composite article according to claim 11 wherein said aluminum hasa thickness of from about 3 mils to about 5 mils.